1. Field of the Invention
This invention relates to a photographic lens barrel suitable for close-up photography using a flash unit and for photography in which the magnification during the close-up photography is photographed on a film.
2. Description of the Prior Art
Having the magnification of a lens photographed on a film along with an object is useful particularly during close-up photography from the viewpoints of analysis, arrangement and the like of photographs. For example, when surgical operations are photographed, photographing of magnification is necessary to judge the size or the like of the affected parts.
Also, when surgical operations are photographed, it is often the case that flash photography is effected in view of the environmental conditions. Therefore, an operation peculiar to the flash unit, for example, the operation of setting an object distance and aperture value corresponding to the guide number, is required.
To meet such a requirement, there have heretofore been separately provided (1) a medical lens of the type in which a plurality of types of close-up lenses are prepared for a fixed focus lens so that a close-up lens corresponding to a desired photographing magnification is selected from among them and is mounted to the fixed focus lens and in which the magnification of the selected close-up lens is manually set and photographed on a film and (2) a lens in which when the guide number of the flash unit is set, the aperture value is varied in accordance with the object distance so as to satisfy the calculation equation of the guide member.
Lenses used exclusively for taking medical photographs are required to have the functions of the both lenses mentioned under items (1) and (2) above, but there have heretofore been no such lenses.